Assignee's U.S. Pat. No. 4,998,240 describes a method and apparatus for remote and unattended testing of customer ISDN lines at an unmanned central office using conventional protocol analyzer equipment. Related patent application Ser. No. 07/646,319 filed Jan. 28, 1991, describes a system and method for remotely testing a plurality of private data network communication lines using a conventional protocol analyzer. Two commercially available protocol analyzers for these purposes are the Bell Atlantic Remote ISDN Protocol Analyzer and the Bell Atlantic Test Systems ( BATS ) Network Analyzer. These are program controlled analyzers. Related Application Ser. No. 07/911,642, filed Jul. 10, 1992, describes a control and port selection arrangement which may be utilized with the BATS protocol analyzers to effect program controlled port selection and control functions is described in that application.
The present invention deals with the testing, monitoring and analyzing of control signaling in Stored Program Control (SPC) switched telephone, data and the like networks. Traditional control signaling in such networks, particularly SPC switched telephone networks has been on a per-trunk or in channel basis. With in channel signaling the same channel is used to carry control signals as is used to carry the call to which the control signals relate. Such signaling begins an the originating subscriber and follows the same path as the call itself.
In current telecommunications and data networks such in-channel signaling is being replaced with Common Channel Signaling (CCS) in which control signals are carried over paths completely independent of the voice channels. The common channel can be configured with the bandwidth required to carry control signals for a large variety of functions. Thus both the signaling protocol and the network architectures to support that protocol are more complex than in channel signaling.
CCS provides a method for exchanging information between Stored Program Control Systems (SPCs) that are inter-connected through a network of signaling links. CCS network nodes may include but are not limited to switching systems, network databases and operator service systems. The current common protocol for CCS is Specification of Signaling System 7 (SS7) which is described in Section 6.5, LSSGR, Issue 2, Jul. 1987, TR-TSY-000506, a module of TR-TSY-000064.
Referring to FIG. 1 there is shown a simplified diagram of an SPC telephone network linking individual subscribers through Central Offices (COs) which are connected by trunks and linked by a typical CCS network. The COs typically consist of a programmable digital switch with CCIS communications capabilities such as an AT&T 5ESS or Northern Telecom DS-100 or the like and may or may not be equipped and programmed to serve as Service Switching Points (SSPs). In FIG. 1 series of central office switches 10, 12 and 14 are shown connected to groups of local subscribers 16, 18 and 20 by conventional local loops or subscriber lines. The COs 10, 12 and 14 are connected by trunk circuits 22 and 24, by way of example. Common Channel Signaling is provided by SS7 data links 26-36 extending between each CO and Signaling Transfer Points (STPs) 38 and 40. These local STPs may be connected to state or regional STPs, not shown.
A pair of STPs is conventionally provided per LATA to provide redundancy so that in the event of failure of one the other immediately assumes its load. Similarly, if one STP becomes overloaded the other shares the load to create a load balance. The paired STPs are connected by C-links so that each STP understands what the other is doing at all times. The STPs may be configured to continually share the load or may be configured in a hot and stand-by capacity. Generally speaking, one will basically monitor the other while they share the load. If one goes down the other is immediately aware of the situation via the C-link and picks up the load to avoid an outage.
Thus each of the COs 10, 12 and 14 are connected to each of the STPs 38 and 40. The STPs provide call processing data transfer between the various COs in the normal manner of SS7 common channel signaling.
In current usage of a CCS network of the type shown in FIG. 1, testing of the CCS or SS7 functioning must be carried out at the particular central office under surveillance in order to permit viewing both of the associated SS7 links at the same time, which is necessary to an effective test. This is ordinarily accomplished using a portable analyzer physically carried to the CO by maintenance personnel. It is only at this CO that the two SS7 links are physically accessible. However, that central office may be many miles distant so that the test may be not only delayed but also highly wasteful of personnel time. In addition, the results of on-site monitoring and collection of data often require more detailed analysis at the maintenance facility. Conveyance of such information to the facility in a timely manner may be costly and inconvenient and yet another trip to the malfunctioning CO may be required.
These problems and disadvantages are multiplied when a central office exhibits a recurring problem that requires extended attention. For example, in a case of network administration, a malfunction may be observed to occur frequently at the same time of day. To diagnose this a technician would have to personally attend the local site each day at the same time until the problem is diagnosed or, alternatively, remain at the site during the entire time of test. As an operating technician is required to be at the testing site, cost considerations restrict use to short, noncontinuous periods. Testing is normally done either on a routine basis or after identification of the existence of a problem whose exact nature is not yet known. Conventional protocol analysis is therefore limited in that it cannot practically be used to monitor the data stream of a selected circuit continuously over an extended period of time. In the absence of such extended monitoring there is no pragmatic way to detect the occurrence of a predefined condition and to initiate a control function upon recognition of such occurrence.